There is developed a technology in which a whole of a device is dipped into liquid coolant and is cooled in order to improve cooling efficiency, regarding a device such as a super computer, a server, a storage or a network component. However, when coolant enters an optical module such as an AOC (Active Optical Cable), optical transmission characteristic of the optical module is degraded.
For example, when coolant enters a space of a jointed portion between ferrules of an optical transceiver, an optical path changes between an edge face of an optical waveguide in one of the ferrules and an edge face of an optical fiber of the other. In this case, optical output is reduced. There is a testing method of leakage using pressure changing on the basis of JISZ2332 of JIS (Japan Industrial Standards), as a testing method of the jointed condition of the ferrules. For example, Japanese Patent Application Publication No. 2005-61999 (hereinafter referred to as Document1) discloses that a SAW device is heated and cooled and leakage is detected.